Ultra high frequency switching device



Nov. 22, 1955 CARTER, JR 2,724,791

ULTRA HIGH FREQUENCY SWITCHING DEVICE Filed June 15, 1952 r j 2 W ,4 L/!6 4 FIG. 2.

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United States Patent-O ULTRA HIGH FREQUENCY SWITCHING DEVICE George E.Carter, In, Danvers, Mass., assignor to Bomac Laboratories Inc.,Beverly, Mass., a corporation of Massachusetts Application June 13,1952, Serial No. 293,247

1 Claim. (Cl. 315-234) This invention relates to ultra high frequencygaseous discharge switching devices, commonly referred to astransmit-receive TR tubes and more particularly to auxiliary means toaid in deionization of the resonant gap after the gaseous discharge.

Such devices are employed in radar systems to decouple the receiverduring transmission of the high power pulse and, thereby protect thesensitive crystals from deterioration or burn-out. In general, TR tubescomprise an evacuated resonant cavity, spaced electrodes forming adischarge gap and a gas fill under reduced pressure. When thetransmitter is on, ionization of the medium in the resonant cavitycauses a short circuit at the gap and because of the circuit arrangementof the TR tube, essentially all of the transmitted pulse is directed tothe antenna.

The position of the TR tube in the system also permits the reflectedreturning signals received by the antenna to be transmitted to thereceiver. The returning signals, however, are at too low a power levelto cause ionization of the gas fill. In passing through the TR tubethese weak signals will be attenuated in proportion to the ionizationremaining after the previous high power transmitted pulse. It is,therefore, necessary that the gap be deionized as rapidly as possibleafter transmission. Recovery time measured in microseconds is the termemployed in the art to express the time interval when deionizationoccurs. Clearer definition and shorter minimum range in the operation ofthe radar system will result from a reduction in recovery time.

Since it is the electrons in the ionized gap that cause most of theattenuation of the reflected signals, their rapid removal is essentialto obtain faster recovery times. It has been noted in the prior art,that a positive potential when applied to an auxiliary electrodeextending into a resonant cavity will aid in the reduction of recoverytime. Such positively biased auxiliary electrodes, however, have alwaysbeen operated at a potential sufiiciently high to cause a self-sustaineddirect current discharge, thereby necessitating the use of a highballasting resistance in series with the direct current voltage supplyand electrode so as to limit the current through the electrode to a safevalue.

According to the teachings of the present invention, a positivepotential below that necessary to cause a se1f sustained direct currentdischarge is applied to an auxiliary electrode. If the impedance of thedirect current voltage source is low to the transient current thatoccurs during the recovery period, a greatly reduced recovery time willbe attained. A direct current voltage source, such as a battery havingan inherent low impedance may be employed, or if the source hasappreciable impedance to high frequency transients, a small condenserbetween the electrode and ground may be used to by pass the voltagesupply.

It is an object of this invention to provide an ultra high frequencygaseous discharge switching device having rapid recovery timecharacteristics.

It is another object of the invention to provide a rapid descriptiontaken in conjunction with the accompanying drawings, in which:

Figure 1 is a longitudinal cross section of the illustrative embodimentof the invention.

Figure 2 is a schematic diagram of the external circuit of the auxiliaryelectrode.

Figure 3 is a schematic diagram of another external circuit of theauxiliary electrode.

The selected illustrative device, as shown in Figure 1, comprises acircular metallic body member 1, defining an evacuated resonant chamber2.

Within said chamber a pair of cones 3 and 4, slightly truncated andaxially disposed from one another, are spaced a predetermined distanceapart to form a discharge gap 5. Cone 3 is axially adjustable by meansof screw 6 which is in threaded engagement with plug 7 and communicateswith flexible diaphragm 8. Cone 4 is hollow to receive one end of anauxiliary electrode. Electrode 9, a component of the circuit of thisinvention, is positioned a short distance from the tip of cone 4 andcommunicates with the discharge gap by means of aperture 10 in the apexof the cone. The other end of electrode 9 extends through a glassreservoir 11 and is positioned in the center of cone 4 by means of aglass to metal seal as at 12. A top cap 13 is provided at the end of theelectrode for connection with the external circuit.

In the illustrative embodiment of this invention, the tip of auxiliaryelectrode 9 is inserted to within approximately .015" of the tip of cone4. As shown in Figure 2, the positive terminal of a direct current lowimpedance voltage source 14, desirably a battery is connected to theauxiliary electrode as shown at 15 with ground at 16. With a potentialof approximately volts or less applied, residual electrons present inthe gap after a discharge will be eifectively swept out of the gaptoward this positively biased electrode.

Further, in the practice of this invention, it is important that thepotential applied be below that necesary to cause a sustained directcurrent discharge of the gas fill employed. With a fill containingapproximately 50 percent argon and 50 percent water vapor under areduced pressure of 12 millimeters of mercury, absolute pressure, adirect current low impedance voltage source of approximately 150 voltsor less will produce the fastest recovery time.

If a high impedance voltage source is employed as represented at 17 inFigure 3, it will be necessary to provide a condenser as at 18 of avalue low enough to assure a low impedance to high frequency transients.This condenser will bypass the voltage supply thereby permitting theresidual electrons to be drawn away from the gap to ground 16. Resultantrecovery times measured with either circuit will be in the order of lessthan one microsecond.

While I have shown and described an illustrative embodiment of myinveion, further variations and modifications will occur to thoseskilled in the art. It is, there fore, my intention to cover, in theappended claims, all such variations and modifications as fall withinthe true spirit and scope of this invention.

I claim:

In combination with a transmit-receive gaseous discharge switching tubehaving a gas-filled envelope, discharge gap electrode structure withinsaid envelope and an auxiliary electrode extending into said envelope,means for providing said tube with rapid recovery time characteristicsof one microsecond or less comprising a direct current voltage sourceelectrically connected to said auxil- 3 iary electrode toprovide apositive bias thereon, said voltage source having a potential below thatnecessary to maintain a direct current-self-sustaining glow discharge inthe regionadjacent the innertiptofsaid auxiliary electrode and acondenser connected between-said auxiliary I electrode and-ground.

4 References Cited in the file of this patent UNITED STATES PATENTS2,404,116 Wolowicz et a1 July 16, 1946 2,526,911 Stone Oct. 24, 19502,544,842 Lawson Mar. 13, 1951 OTHER REFERENCES Proc. I. R. E., vol. 39,No. 12, Dec. 1951, pp. 1493- 1501; see p. 1499, col. 1 in particular.

